Electrically-powered vehicles have a long history. Electrically-powered pantograph trains are used for commuter passenger trains along heavily traveled routes on the east coast of the United States and in the Chicago metropolitan area. Subways and other light rail systems routinely use electrified third-rail systems. Electrically-powered automobiles and delivery vans are in use around major cities. Electrically powered golf carts, fork lift trucks and other such specialized vehicles also exist.
Electrical power offers numerous benefits as an energy source in transportation. In railroad locomotives, electric motors offer excellent low end torque, reliability and ease of maintenance. Diesel-electric locomotives use diesel engines to turn generators, which in turn supply electrical power to drive electric traction motors in order to gain these advantages. Still other advantages can be gained by the use of purely electric-powered vehicles. Examples of such advantages include reduced pollution output, reduced mechanical complexity and, where the electrical power source is external, reduced weight.
Unfortunately, providing adequate electrical power to vehicles has proven difficult, expensive, or inconvenient, or all three of the above depending upon the application. Pure electrically-powered vehicles have conventionally used one of two sources of electrical power, on-board batteries or external sources such as trolleys. Batteries are inefficient stores of energy, particularly when compared to gasoline, which limit the relative range of vehicles using batteries. The batteries required by a vehicle for even limited ranges of 50 to 100 miles add considerably to the weight of the vehicle using them, adding inherent inefficiency to the vehicle. Providing external sources of power, such as trolley systems, has typically required a prohibitive capital investment and has limited the routing of vehicles.
Nonetheless, electrically powered transportation systems employing external power sources have been very successful where employed. Electrified rail systems have typically relied on external power. External electric power supplies such as overhead trolleys and third rail systems work well for railroads under certain conditions. However, overhead lines are extremely expensive and considered by many to be unsightly. In many environments overhead lines are exposed to possible damage from weather, accident and sabotage. Third rail systems work well but are inherently dangerous to pedestrians. None of these systems have proven economically viable for lightly traveled routes despite wide appreciation of the reduced pollution and reduced maintenance costs afforded by such systems.
Electrification of automobiles and other over the road motor vehicles has progressed even more slowly than in the railroad industry. In fact, electrification of automobiles has regressed since the beginning of the century when electric vehicles vied with internal combustion powered and external combustion powered vehicles for dominance on the highways. Practical electric automobiles have typically been supplied with energy from batteries. At best, batteries provide energy to travel about one hundred miles. The use of accessories such as heat, air conditioning, or headlights, greatly reduces even this limited range. The weight of the batteries themselves reduces the range, and space efficiency of automobiles so equipped. Frequent recharging of the batteries in such vehicles is unavoidable. In addition, many of the best batteries in terms of overall energy storage capability accept charging at a slow rate. This makes recharging a slow and tedious affair. Electrically-powered battery equipped automobiles have proven inconvenient compared to internal combustion powered motor vehicles.
Battery equipped vehicles compare very poorly in efficiency terms with electric vehicles energized by external electrical sources. For this reason numerous inventors have attempted to develop systems for delivering electrical power to over the road vehicles. Such systems have typically had the disadvantages of high initial capital cost, plus the additional handicap of overly limiting the maneuverability of the vehicles so powered. With the exception of trolley buses, practical electrically-powered motor vehicles have carried a heavy load of storage batteries as a power source. Guidance control of the trolley has also complicated use of external electrical power in cars.
U.S. Pat. No. 1,859,343, teaches an electric vehicle having electrically conductive tires. The conductive tires contact a series of conductors embedded in a roadway to complete an electric circuit between the embedded conductors and an overhead line which is engaged by a trolley. While this system allows limited maneuverability, it has the same basic limitations of any overhead trolley system.
U.S. Pat. No. 4,139,071 provides an electrified traffic lane having at least two spaced parallel contact assemblies mounted with their top surfaces flush with the road on each side of the vehicle. The contact assemblies each require a predetermined weight thereon to maintain electrical contact with the vehicle wheels. The vehicle employs electrically-conductive tires which are the pickup contact with the conductors for energization of electrical motors within the vehicle. This system presents a safety hazard to potential foot traffic along the roadway in that the system can be energized by any adequate weight and remains energized when a stationary weight is on a roadway electrical contact assembly.
U.S. Pat. No. 4,476,947 attempted to answer these difficulties. More particularly, the patent proposed a system directed to electrification of roadways and which provided vehicles adapted to receive power from such roadways for motive power and for recharging a minimal battery pack for powering the vehicle for off electrified roadway operation.
The patent proposes an electrified roadway which includes sets of paired, parallel, sectioned power rails. Each pair of power rails is aligned with a traffic lane of the roadway. Sections of each pair correspond to one another. Corresponding sections are energized with opposite polarity D.C. power according to the presence of a vehicle and demand by the vehicle for power. Vehicles are provided with a pair of trolleys, aligned perpendicular to the direction of movement of the vehicle. A powered guidance mechanism is provided for maintaining trolley tracking of the power rails.